Aims. We investigate the dust-to-gas mass ratio and the environmental effects on the various components of the interstellar medium for a spatially resolved sample of Virgo spirals. Methods. We have ...used the IRAM-30 m telescope to map over their full extent NGC 4189, NGC 4298, NGC 4388, and NGC 4299 in the (CO)-C-12(1-0) and the (CO)-C-12(2-1) lines. We observed the same lines in selected regions of NGC 4351, NGC 4294, and NGC 4424. The CO observations are combined with Herschel maps in 5 bands between 100-500 mu m from the HeViCS survey, and with HI data from the VIVA survey, to obtain spatially resolved dust and gas distributions. We studied the environmental dependencies by adding to our sample eight galaxies with (CO)-C-12(1-0) maps from the literature. Results. We estimate the integrated mass of molecular hydrogen for the galaxies observed in the CO lines. We find molecular-to-total gas mass fractions between 0.04 \textless= f(mol) \textless= 0.65, with the lowest values for the dimmest galaxy in the B-band. The integrated dust-to-gas ratio ranges between 0.011 and 0.004. For the 12 mapped galaxies we derive the radial distributions of the atomic gas, molecular gas, and dust. We also study the effect of different CO-to-H-2 conversion factors. Both the molecular gas and the dust distributions show steeper radial profiles for HI-deficient galaxies and the average dust-to-gas ratio for these galaxies increases or stays radially constant. On scales of similar to 3 kpc, we find a strong correlation between the molecular gas and the 250 mu m surface brightness that is tighter than average for non-deficient galaxies. The correlation becomes linear if we consider the total gas surface mass density. However, the inclusion of atomic hydrogen does not improve the statistical significance of the correlation. Conclusions. The environment can modify the distributions of molecules and dust within a galaxy, although these components are more tightly bound than the atomic gas.
We use Herschel PACS and SPIRE observations of the edge-on spiral galaxy UGC 4754, taken as part of the H-ATLAS SDP observations, to investigate the dust energy balance in this galaxy. We build ...detailed SKIRT radiative models based on SDSS and UKIDSS maps and use these models to predict the far-infrared emission. We find that our radiative transfer model underestimates the observed FIR emission by a factor of two to three. Similar discrepancies have been found for other edge-on spiral galaxies based on IRAS, ISO, and SCUBA data. Thanks to the good sampling of the SED at FIR wavelengths, we can rule out an underestimation of the FIR emissivity as the cause for this discrepancy. Instead we support highly obscured star formation that contributes little to the optical extinction as a more probable explanation.
We present the results of large-area {sup 12}CO J = 3-2 emission mapping of three nearby field galaxies, NGC 628, NGC 3521, and NGC 3627, completed at the James Clerk Maxwell Telescope as part of the ...Nearby Galaxies Legacy Survey. These galaxies all have moderate to strong {sup 12}CO J = 3-2 detections over large areas of the fields observed by the survey, showing resolved structure and dynamics in their warm/dense molecular gas disks. All three galaxies were part of the Spitzer Infrared Nearby Galaxies Survey sample, and as such have excellent published multiwavelength ancillary data. These data sets allow us to examine the star formation properties, gas content, and dynamics of these galaxies on sub-kiloparsec scales. We find that the global gas depletion time for dense/warm molecular gas in these galaxies is consistent with other results for nearby spiral galaxies, indicating this may be independent of galaxy properties such as structures, gas compositions, and environments. Similar to the results from The H I Nearby Galaxy Survey, we do not see a correlation of the star formation efficiency with the gas surface density consistent with the Schmidt-Kennicutt law. Finally, we find that the star formation efficiency of the dense molecular gas traced by {sup 12}CO J = 3-2 is potentially flat or slightly declining as a function of molecular gas density, the {sup 12}CO J = 3-2/J = 1-0 ratio (in contrast to the correlation found in a previous study into the starburst galaxy M83), and the fraction of total gas in molecular form.
Passive early-type galaxies (ETGs) provide an ideal laboratory for studying the interplay between dust formation around evolved stars and its subsequent destruction in a hot gas. Using Spitzer-IRS ...and Herschel data we compare the dust production rate in the envelopes of evolved AGB stars with a constraint on the total dust mass. Early-type galaxies which appear to be truly passively evolving are not detected by Herschel. We thus derive a distance independent upper limit to the dust grain survival time in the hostile environment of ETGs of \textless46 +/- 25 Myr for amorphous silicate grains. This implies that ETGs which are detected at far-infrared wavelengths have acquired a cool dusty medium via interaction. Given likely time-scales for ram-pressure stripping, this also implies that only galaxies with dust in a cool (atomic) medium can release dust into the intra-cluster medium.
We present a resolved dust analysis of three of the largest angular size spiral galaxies, NGC 4501 and NGC 4567/8, in the Herschel Virgo Cluster Survey (HeViCS) science demonstration field. Herschel ...has unprecedented spatial resolution at far-infrared wavelengths and with the PACS and SPIRE instruments samples both sides of the peak in the far infrared spectral energy distribution (SED). We present maps of dust temperature, dust mass, and gas-to-dust ratio, produced by fitting modified black bodies to the SED for each pixel. We find that the distribution of dust temperature in both systems is in the range similar to 19-22 K and peaks away from the centres of the galaxies. The distribution of dust mass in both systems is symmetrical and exhibits a single peak coincident with the galaxy centres. This Letter provides a first insight into the future analysis possible with a large sample of resolved galaxies to be observed by Herschel.
The Sombrero galaxy (NGC 4594) is an Sa galaxy with a symmetric dust ring. We have used the Large APEX BOlometer CAmera (LABOCA) at 870 μm and the MAx-Planck Millimeter BOlometer (MAMBO-2) at 1.2 mm ...to detect the dust ring for the first time at submillimetre and millimetre wavelengths. We have constructed a model of the galaxy to separate the active galactic nucleus (AGN) and dust ring components. The ring radius at both 870 μm and 1.2 mm agrees well with the radius determined from optical absorption and atomic gas studies. The spectral energy distribution of the ring is well fitted by a single grey-body with dust emissivity index $\beta=2$ and a dust temperature $T_{\mathrm d}=18.4$ K. The dust mass of the ring is found to be $1.6\pm0.2\times 10^7$ $M_\odot$ which, for a Galactic gas-to-dust ratio, implies a gas mass that is consistent with measurements from the literature.
We present the dust properties of a small sample of Virgo cluster dwarf galaxies drawn from the science demonstration phase data set of the Herschel Virgo Cluster Survey. These galaxies have low ...metallicities (7.8 \textless 12 + log(O/H) \textless 8.3) and star-formation rates \textless= 10(-1) M-circle dot yr(-1). We measure the spectral energy distribution (SED) from 100 to 500 mu m and derive dust temperatures and dust masses. The SEDs are fitted by a cool component of temperature T \textless= 20 K, implying dust masses around 10(5) M-circle dot and dust-to-gas ratios D within the range 10(-3)-10(-2). The completion of the full survey will yield a larger set of galaxies, which will provide more stringent constraints on the dust content of star-forming dwarf galaxies.
Supernova (SN) explosions are crucial engines driving the evolution of galaxies by shock heating gas, increasing the metallicity, creating dust, and accelerating energetic particles. In 2012 we used ...the Atacama Large Millimeter/Submillimeter Array to observe SN 1987A, one of the best-observed supernovae since the invention of the telescope. We present spatially resolved images at 450 mu m, 870 mu m, 1.4 mm, and 2.8 mm, an important transition wavelength range. Longer wavelength emission is dominated by synchrotron radiation from shock-accelerated particles, shorter wavelengths by emission from the largest mass of dust measured in a supernova remnant (>0.2 M sub(middot in circle)). For the first time we show unambiguously that this dust has formed in the inner ejecta (the cold remnants of the exploded star's core). The dust emission is concentrated at the center of the remnant, so the dust has not yet been affected by the shocks. If a significant fraction survives, and if SN 1987A is typical, supernovae are important cosmological dust producers.
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